1. Field of the Invention
This invention relates to the field of thermal power plants, specifically of the type that recycle a significant portion of the heat that is normally rejected to the environment by “conventional” thermal power plants.
2. Description of the Prior Art
A search of the prior art reveals numerous inventions that attempt to improve the efficiency of various types (e.g., Rankine cycle, Stirling cycle, Brayton cycle, Otto cycle, Diesel cycle, Seebeck cycle, etc.) of heat engines and the thermal power plants in which they are contained.
In 1824, Nicolas Leonard “Sadi” Carnot, a French engineer and founder of the discipline now known as “Thermodynamics,” published his treatise (Reflexions sur la puissance motrice du feu et sur les machines propres a developper cette puissance) on the nature of heat engines. The relevant finding of this paper was that all heat engines, in order to function, first receive heat from a “high-temperature” heat source, and then must reject heat (i.e., unused heat, a.k.a. waste heat) to a “low-temperature” heat sink. He also gave us what is now known as the “Carnot Efficiency,” which states that the efficiency of a heat engine is improved as the temperature differential between the heat source and the heat sink is increased. In the decades that followed, others expanded upon and clarified our understanding of the nature of heat, and how best to employ it in heat engines. Most notable among them was an engineering professor from Scotland named William J. M. Rankine, who in 1859, published his treatise (Manual of the Steam Engine and Other Prime Movers) relating to heat engines, wherein he described what is now known as the “Rankine cycle.” Later, still others expanded upon the ideas postulated by Prof Rankine, a process that continues to the present day.
The Rankine cycle itself is inherently inefficient, yet it has attributes, which have caused it to become one of the leading forms of heat engine cycles employed today. First, the Rankine cycle is well understood by the designers and users of power generation equipment. Second, the Rankine cycle lends itself well to the employment of very large and therefore very cost-effective components. Third, with the exception of “hydro-power” nothing can produce electrical power less expensively than a modern electrical power generating station employing a “modified” Rankine cycle.
The latest attempts to improve upon the Rankine cycle employ various forms of “co-generation;” i.e., they attempt to convert a portion of the waste heat rejected by a “host” heat engine into additional electrical power, industrial process heating, and/or air conditioning capacity. The latter two approaches, while beneficial are not very practical, for it is a rare or non-existent industrial process that would require all of the waste heat being liberated by the “host” heat engine. Similarly, the air conditioning capacity approach, while quite ingenious, has two burdens hindering its widespread use, first the “host” heat engine needs to be located near the facility to be cooled, and second, air conditioning is not a “stable” demand (i.e., high demand in the summer, and low demand in the winter). Which leaves the additional electrical power approach as the only economically viable method for improving the efficiency of thermal power plants.
There exists a class of heat engines known as “Bottoming Cycle Heat Engines,” many of which include components referred to as “Heat Recovery Steam Generators” or HRSG's. Essentially, their designers have placed a second Rankine cycle heat engine in the waste heat stream of the “host” heat engine, and while it is the “environmentally friendly” thing to do, financially it is not very attractive. This approach is costly and does not provide the kind of returns that most electric utility shareholders are looking for on the bottom line of their financial statements.
One of the principal reasons for the resistance to these devices is that they involve extensive and therefore expensive redesigns of existing facilities; as a result they are not being widely used to rehabilitate older power plants. New facilities, currently under construction, are just now starting to incorporate some of these design elements, yet the larger opportunity is to retrofit the worldwide base of currently operating electrical power generating facilities. To do this, a design approach that accomplishes the following key points must be employed: the design must be environmentally friendly, the design must not require expensive changes to the “host” facility, the design must be reliable, and the design must produce an acceptable financial return. Such a design will meet with success, to date, not a single example of the prior art has satisfied all of these requirements.